[channels] Inconsistent use of capital letters in channel manager UI labels

Inconsistent use of capital letters in labels.

"Edit Channel"
"Publish my changes"
"Discard my changes"
"Manage Changes"
"Full screen"
"Save & Close"
"Edit content"
"Edit menu"
"Page Settings"
"Page title"
"Channel Settings"
"Website Properties"
"Add new page"

Many software applications use a capital letter for all principal words in labels, but not for connecting words. See e.g. Jira. Some labels in the channel manager use this pattern, e.g. "Edit Channel", other do not, e.g. "Publish my changes".

Whatever pattern is chosen, it should be used consistently.